There are various similar services like REVAIN, but they are not on the blockchain and therefore, the reviews on them can be biased. I think this will allow attracting only quality projects to this review platform. Otherwise, you can easily get a negative review. Bounty members can check it out for themselves. Write a reviews and get a rewards, what could be easier?
Blockchain is a new technology, so why not use it? I fully support the idea of making such a project on the blockchain, which will give maximum transparency and at the same time safety.